CBD was shown to improve bone quality in OVX mice when administered as an early intervention. In C57BL/6 J mice, CBD (25 mg/kg/day, perorally administered 5 days/week for 18 weeks) restored OVX-induced reductions in whole-body and femoral areal BMD (aBMD), improved trabecular quality, and improved markers of bone metabolism [25]. In Sprague–Dawley rats, CBD supplementation (5 mg/kg/day, administered 13 weeks after surgeries via IP injection (5 days/week for 3 weeks) improved femoral BV/TV% (bone volume/total volume of bone) and Tb.N (mean trabecular number), as well as maximum force in femurs and vertebrae, but there was no difference in femoral BMD or expression of receptor activator of nuclear factor kappa-Β ligand (RANKL) and osteoprotegerin (OPG) between the CBD and vehicle treated groups [26]. In contrast, CBD treatment administered by osmotic pump (5 mg/kg/day for 12 weeks) did not restore OVX-induced trabecular bone loss or reduce circulating markers of bone resorption in skeletally mature Sprague–Dawley rats [27]. Differences in the outcomes of these studies may be due to differences in route of CBD administration and potential for interaction of phytocannabinoids and the gut microbiome, as well as age at time of ovariectomy, i.e., during growth vs. maturity. Orally consumed CBD is likely biotransformed by gut bacteria [28] and the effects of the resulting microbial metabolites on bone and other tissues remain to be investigated. Additional research is required to determine the optimal timing and dosage of CBD for mitigating OVX-induced bone loss.

Several rodent studies have shown that CBD may promote bone healing, while other phytocannabinoids are effective for pain management but have mixed effects on bone. When the effects of OVX and CBD on femoral fracture healing were examined C57BL/6 J mice, CBD treatment (5 mg/kg, administered via osmotic pump) that was initiated prior to, but not at the time of the fracture, reduced OVX-induced delayed bone healing [29]. CBD pretreatment did not enhance bone quality or strength in healthy male mice with femoral fractures, but restored fluoxetine-induced reductions in BMD [29]. In a surgical model of spinal cord injury in male Wistar rats, CBD (5 mg/kg/day) administered by IP injections starting 12 h post-surgery for 14 days resulted in increased osteocalcin and reduced collagen type I cross-linked telopeptide in serum, and improved femoral BMD, trabecular quality, and mechanical properties [30]. In male Wistar rats that underwent radial bone ostectomy, treatment with an osteoconductive scaffold containing CBD-loaded microspheres promoted new bone formation, mesenchymal stem cell migration, and increased expression of osteogenic markers compared to control CBD-free scaffold [31]. In a mouse model of collagen-induced arthritis, male DBA/1 J mice that received subcutaneous injections of Δ−8-THC (30 mg/kg, twice per day for 2 weeks) had reduced pain, ankle joint inflammation, and bone erosion [32]. Very few studies have directly compared the effects of different phytocannabinoids which are expected to have divergent effects on bone due to their distinct chemical structures and receptor binding profiles. In female Sprague–Dawley rats with lumbar fusion, histological analysis showed CBD treatment (IP injections of 5 mg/kg/week for 8 weeks) improved bone healing and new bone formation [33]. Osteogenic factors were upregulated after 2 weeks but not 8 weeks, which suggests CBD enhances bone formation in the early stages of healing [33]. In contrast, bone healing was unchanged in rats receiving THC alone or a combination of CBD and THC [33]. In male Sprague–Dawley rats, CBD but not THC treatment (IP injections of 5 mg/kg/day for 2, 4, 6, or 8 weeks) improved maximal load and work-to-failure [34]. CBD increased Plod1 (lysyl hydroxylase 1) mRNA expression, an enzyme required for collagen synthesis, in primary osteoblast cultures, and may enhance collagen crosslinking [34]. The effect of THC and CBD osteoclast fusion and bone resorption in human osteoclasts was shown to be dose dependent. At lower doses (0.3 to 10 µM), THC and CBD increased bone resorption, but osteoclast fusion was unaffected while at higher doses (10 and 30 µM) osteoclast fusion and bone resorption were inhibited [35]. In vitro studies demonstrated that CBD may support bone regeneration by increasing osteogenic differentiation and reducing osteoclast activity. CBD promoted osteoblast differentiation through p38 MAPK activation in U2OS and MG-63 cells [36], increased cell viability and proliferation and osteocalcin expression in human skeletal stem and progenitor cells (SSPCs) [29], and suppressed tumor-induced osteoclastogenesis [37].

Phytocannabinoids show promise as alternatives to NSAIDs and opioids for fracture pain management; however, their effects during fracture healing are insufficiently investigated. A mouse model of tibial fracture was used to compare the analgesic effects of CBD, CBG, and CBC [38, 39]. CBD and CBG increased bone volume fraction, BMD, and strength and decreased pain [38] while CBC was beneficial for pain management but inhibited bone repair [39].

Studies have investigated CBD in rodent models of periodontitis and suggest phytocannabinoids may support periodontal health. CBD administered by IP injection (5 mg/kg/day for 30 days) attenuated periodontitis-induced alveolar bone loss, inhibited RANK/RANKL expression, and reduced markers of inflammation in male Wistar rats [40]. In male Sprague–Dawley rats, oral treatment with CBD (20 mg/kg/d) in combination with taurine (100 mg/kg) for 21-days reduced periodontal inflammation, pocket depth, and alveolar bone loss [41]. Topically applied CBD (100 mg/kg/day for 4 weeks) inhibited TLR4/NFkB signaling to prevent bone loss and periodontitis-induced inflammation in male Sprague Dawley rats [42]. In vitro studies demonstrated that CBD may protect against alveolar bone resorption by promoting osteogenic differentiation. In human tori-derived bone stromal cells, ex vivo treatment with CBD enhanced osteogenic differentiation, biomineralization, and increased mRNA expression of runt-related transcription factor 2 (RUNX2), bone sialoprotein (BSP), and Osterix [43]. Pretreatment with an AKT inhibitor or β-catenin antagonist reduced these changes, suggesting AKT/β-catenin may be required for CBD to improve osteogenesis [43]. Dental pulp stem cells (DPSCs) are an emerging therapeutic in regenerative dentistry, and recent findings suggest CBD can enhance DPSC function [44–46]. CBD increased DPSC viability, migration, and osteogenic/odontogenic differentiation, and had a pro-angiogenic and anti-inflammatory effect [45]. CBD upregulated osteogenic differentiation and expression of osteogenic markers in DPSC-derived organoid-like microspheroids which promoted bone healing in a nude mouse calvarial defect model [46]. The effect of other phytocannabinoids on bone health remains to be investigated. There has only been one study which demonstrated THC may be beneficial for preventing alveolar bone loss [47], but no studies of other minor cannabinoids. Periodontal width narrowing and bone resorption caused by tooth movement was reversed by treatment with dronabinol, a synthetic THC (10 mg/kg/day for 21 days by IP injection) [47].

Most of the studies investigating the effects of phytocannabinoids on bone have used isolated CBD and there is limited research using extracts containing multiple phytocannabinoids. In a study that used destabilization of the medial meniscus (DMM) surgery to stimulate osteoarthritis in male C57BL/6 J mice, CBD (20 mg/kg/day) and CBD + CBG (10 mg CBD and 10 mg CBG/kg/day) oils reduced pain and inflammation and normalized locomotor activity but did not affect bone remodeling [48]. DMM mice treated with CBG, but not CBD, demonstrated reduced cartilage degeneration, chondrocyte loss, and matrix metalloproteinase-13 expression, suggesting CBG oil is chondroprotective [48].

There is limited data on the effect of cannabis on bone. Male Wistar rats with tibial titanium implants that were forced to inhale cannabis smoke for 8 min per day for 60 days showed decreased trabecular bone healing around the implants, but there was no effect on cortical bone [49]. How bone may be affected by cannabis may depend on factors such as route of administration (smoking, oral, topical, etc.,), age and sex, and hormone status, however this remains to be investigated.